Control device



Aug. 1, 1939. L. R. KOLLER ET AL 2,168,165

CONTROL DEVICE Filed March 26, 1938 Fig-.3.

'5 55' E BC. 3 O X I I CATHODE EMISSION Z [1.] o: m D o lnyntorsz 1 Levws RKoller", I00 I CONVI'ROL ems VOLTAGE 0 Ralph PJOhTWSOTW,

by Cf. Them Attorney.

Patented Aug. 1, 1939 2,168,165

UNITED STATES PATENT OFFICE CONTROL DEVICE Lewis B. Koller and Ralph P. Johnson, Schenectady, N. Y., assignors to General Electric Company, a corporation of New York Application March 26, 1938, Serial No. 198,339

Claims. (01. 250-27) The present invention relates to an improved potential will be positive with respect to the control device, which has a definite lock-out cathode. characteristic; that is, which acts positively in Assume, however, that some means is provided such a way as to prevent chattering. for varying the primary electron current from The features of novelty which We desire to prothe cathode C as, for example, by varying the 5 tect herein will be pointed out with particularity emission of the cathode C. If this means is perin the appended claims. The invention itself, mitted to reduce the value of the primary curtogether with further objects and advantages rent Ip, the secondary current Is would necesthereof, may best be understood by the following sarily be proportionately decreased. Their difdescription taken in connection with the drawference also will be diminished and the poteno ing, in which Fig. 1 is a schematic representatial of the electrode P will drop, thus lessening tion useful in explaining the principle of operastill further the number of secondary electrons tion of the invention; Fig. 2 shows diagrammatiemitted by it. (It will be observed that the eleccally one practical embodiment of the invention; trode potential is thus predominantly a function Fig. 3 illustrates graphically the operating charof the primary electron current.) When a con- 5 acteristics of the device of Fig. 2; Fig. 4 shows dition is reached at which the second electron an alternative embodiment of the invention, and current is precisely equal to the primary elec- Fig. 5 illustrates the operating characteristics of tron current, it is clear that the current flowing the device of Fig. 4. through the resistance R will be zero and the The invention makes use of secondary emispotential of the electrode P will be equal to that sion, that is to say, the emission of electrons of the cathode C. Under these conditions the from an electrode surface in response to the imlatter electrode can receive no primary elecpingement of primary electrons on such surface. trons since such electrons will be repulsed by The manner in which this phenomenon is utiits electrostatic field, and the tube will cease to lized is indicated in Fig. 1. become conductive (assuming always that the In the arrangement shown, there is provided anode A cannot be reached by primary electrons a cathode C which acts as a source of primary alone). Furthermore, the tube cannot be reenelectrons; a secondary emission electrode P ergized by merely increasing the potential of adapted to receive primary electrons and to the anode A, or by raising the emissivity of the generate secondary electrons as a result of the cathode C, since neither of these steps will be primary electron flow thereto, and an anode A effective to raise the potential of the secondary adapted to receive secondary electrons emitted emission electrode P to a value at which it can from the surface of the electrode P. It is asreceive electrons. The device described theresumed that the anode A is so constructed and fore has an inherent lock-out characteristic in arranged that it collects few, if any, of the prithat it tends to become completely non-conducmary electrons. A battery B connected between tive at a certain critical value of the primary the cathode and anode serves to maintain the current. This value is adjustable by regulation latter at a positive potential with respect to the of the value of the resistance R.

former. The connection between the cathode A practical application of the invention is and the secondary emission electrode P includes illustrated in the more complete circuit of Fig. 0

a high resistance R. 2 in which there is shown a cathode ID of lighte d v y be ght to a conductive sensitive character, that is, variable in emission state by instantaneously applying positive p0 in accordance with the intensity of light imtential to the electrode P (from a source not pinging on its surface. Opposite this electrode shown). Thereafter, the electrode simultaneand in cooperative relation therewith there is 45 ously receives a stream of primary electrons Ip provided a secondary emission electrode ll corfrom the cathode and emits a stream of secondresponding in function to the element P deary electrons Is which proceeds to the anode A. scribed in connection with Fig. 1. From a con- Consequently, the current which flows in the structional standpoint this latter electrode need external circuit connected to the electrode P has have no unusual characteristics since most elec- 50 a value represented by the difference quantity trode surfaces are adapted to emit secondary Is-Ip. This current serves to fix the potential electrons to a degree sufiicient for the purposes of of the electrode P by virtue of the voltage drop the present invention. It may comprise, for exwhich it creates across-the resistance B. As long ample, a metal plate constituted of nickel, or

the value Is is greater than the value Ip this the like. 55

Interposed between the cathode l0 and the electrode ll there is provided a grid-like anode l3. This may receive some primary electrons but is intended to be energized primarily by secondary electrons which are emitted by the electrode II in response to the impingement thereon of primary electrons from the cathode. This anode is maintained at positive potential with respect to the cathode by means of a battery l4 and is connected to a utilization circuit comprising a load device l5 which is to be energized by current flowing from the anode. device may comprise, for example, a relay adapted to control any type of energy-translating apparatus such, for example, as a motor, a lamp circuit, or a heating system.

Between the cathode l0 and the anode l3 there is provided a space charge grid I! having a function which will shortly be described. This may be connected to the secondary emission electrode H either directly, as shown, or through the intermediation of a battery adapted to maintain a desired biasing potential on the grid. A circuit including a resistance l8, which has a value preferably, but not necessarily, on the order of 10 to 10 'ohms, serves to connect the cathode to the'grid ll and to the electrode H.

As previously stated, the current received by the anode I3 is a function of the primary current impinging on the secondary emission electrode i I. In the arrangement illustrated, this primary current is caused to be variable in response to a controlling infiuence by'the provision of a system including a lens 20. for focusing on the surface of the cathode H! a light. beam whose intensity tends to approach a predetermined critical value. The source of the light beam. may be chosen with relation to the element desired to be controlled; That is, for example, if the device is to control a street lighting circuit, the cathode Ill may be exposed to a. source of daylight so as to permit energization of the lighting circuit in response to decrease of daylight intensity below a predetermined level.

The value of the resistance l8 is so selected that at a predetermined desired value of primary electron current, the potential of the secondary emission electrode II will become equal to that of the cathode. As soon as this occurs the space charge grid 11, which also attains the potential of the cathode, serves to prevent any further flow of primary electron current. Thus, it exerts a blocking actionso that the supply of current to the utilization circuit is'cut off.

As previously explained in connection with Fig. 1, a. device of this kind cannot be made again conductive simply by increasing the emission of the cathode Ill. Consequently, there is no tendency for the control to chatter or hunt, if the controlling influence fluctuates about its critical value. In order to reenergize the load device when such reenergization becomes desirable, one may impress on the secondary electrode H a potential above that of. the cathode l8. This may be accomplished, for example, by means. of a switch 22 for instantaneously connecting the electrode to the positive terminal. of the battery l4. After conductivity is established the device may again be rendered responsive to the control influence by opening the switch 22.

The characteristic of a device such as that just described is illustrated in Fig. 3 wherein the curve E represents the variation of current to. the anode 13 with changes in cathode emission. It will be noted that the anode current decreases This relatively slowly until a critical point a: is reached at which it drops abruptly to zero. This point corresponds to the value of the cathode emission at which the potential of the secondary emission electrode l becomes equal to that of the cathode.

The arrangement of Fig. 4 differs from that just described mainly in respect to the means provided for controlling the primary electron current. In this case the cathode is represented as comprising a filament 24 connecting with a battery 25 which supplies heating current to the filament. The filament is assumed to have substantially constant emission.

Spaced from the cathode there are provided a secondary emission electrode 2?, a grid-like anode 2B and a space charge grid 29. These elements correspond in essential particulars to the similar elements described in Fig. 4. A battery 3| in series with a load device 32 is connected between the cathode 24 and the anode 28. A resistance 33 serves to fix the potential of the electrodes 21 and 29. in the manner previously explained.

Between the cathode 24 and the space charge grid 29 there is provided a control grid 35 which acts to regulate the flow of primary electrons from the cathode 24. This grid may be biased to a suitable potential by means of a battery 35 and is rendered responsive to a control influence by means of a control device connected in circult with the grid as indicated at 31. The element, 3! may comprise any known type of device for varying the potential of the grid 35 in accordance with variations in an electrical or physical condition such as the condition of an electrical circuitpr the condition of a heating device or the like.

Ihe operating characteristic of a device such as that. shown. in Fig. 4 is illustrated in Fig. 5 in which curve F represents the variations in current to the anode 28 with changes in the potential applied to the control grid 35. The dotted reference line depending downwardly from point y of curve F indicates a cut-off action of the device of Fig. 4 occurring at a negative control voltage corresponding to the value 1/. This is the characteristic which might be obtained with a given resistance R1. The cut-off point may be shifted, for example to a point Z, by employing a different and higher resistance R2 between the cathode 24 and the secondaryemission electrode 21-. It will be understood that the control grid voltage is measured from the zero axis at the right of the representation of Fig. 5 and increases in negative magnitude as one proceeds to the left.

The device may be restarted after cut-off action by closing the normally open switch 39 so as to apply positive potential to the electrodes 2! and 29.

The devices which we have described are unusual in their rapidity of response. Particular devices, which we have tested have proven to be capable of lock-out, action in less than one micro second after the application of a favorable controlling potential. Furthermore, the rapidity of response can be Varied by shunting by a condenser the resistance which connects the cathode to the secondary emission electrode.

While we have described our invention primarily in its operation as a control device it will be understood that it is capable of other applicationswhere a discharge device having an extremely sharp cut-off characteristic is desired. We aim inthe, appended claims to cover all equivalent modifications and applications which come within the true spirit and. scope of the foregoing disclosure.

What we claim as new and desire to secure by Letters Patent of the United States, is:

1. In combination, a source of primary electrons, an electrode emitting secondary electrons only in response to the flow thereto of primary electrons from said source, an anode arranged to receive current only upon the occurrence of secondary emission from the said electrode, a utilization circuit connected to said anode and energized by the current received thereby, means for varying the primary electron current, the said means being responsive to a controlling infiuence which tends to approach a predetermined critical value, and means for causing the abrupt deenergization of the utilization circuit upon the attainment of the said predetermined critical value of the controlling influence, said last named means including an impedance connection between said electrode and said source for making their potential difference predominantly a function of the primary electron current flowing be tween them, and means dependent on said potential difference for completely blocking the flow of primary electrons upon the attainment of the said predetermined critical value of the controlling influence.

2. In combination, an electron emissive cathode, an electrode for emitting secondary electrons in response to the impingement thereon of primary electrons from said cathode, a grid interposed between the cathode and the secondary emission electrode and electrically connected to the latter, a grid-like anode between the grid and the secondary emission electrode for receiving secondary electrons from the latter, a load device connected in circuit with the anode, means for varying the primary electron current, the said means being responsive to a controlling influence which tends to approach a predetermined critical value, and means including a resistance connecting the cathode to the grid and the secondary emission electrode for making the potential level of the latter elements predominantly a function of the primary electron current, the resistance being such that upon the attainment of the said predetermined value of the controlling influence the potential of the grid becomes effective completely to block the flow of primary electrons and thus to prevent the further supply of current to the load device.

3. In combination, an electron emissive cathode, an electrode for emitting secondary electrons in response to the impingement thereon of primary electrons from said cathode, a grid interposed between the cathode and the secondary emission electrode and electrically connected to the latter, a grid-like anode between the grid and the secondary emission electrode for receiving secondary electrons from the latter, a load device connected in circuit wtih the anode, means for varying the emission of the cathode, the said means being responsive to a controlling influence which tends to approach a predetermined critical value, and means connecting the cathode to the grid and the secondary emission electrode for making the potential level of the latter elements predominantly a function of the primary electron current, the last-named means being of such nature that upon the attainment of the said predetermined value of the controlling influence the potential of the grid becomes efiective completely to block the flow of primary electrons and to prevent the further supply of current to the load device.

4. A control device comprising a cathode having its emissivity variable in accordance with the intensity of the light to which it is exposed, an electrode for emitting secondary electrons in response to the impingement thereon of primary electrons from said cathode, a grid interposed between the cathode and the secondary emission electrode and electrically connected to the latter, a grid-like anode between the grid and the secondary emission electrode for receiving secondary electrons from the latter, a load device connected in circuit with the anode, and means including a resistance connecting the cathode to the grid and the secondary emission electrode for making their potential level predominantly a function of the primary electron current, the resistance being such that for a predetermined light exposure of the cathode the potential of the grid becomes eiTective completely to block the flow of primary electrons and thus to prevent the further supply of current to the load device.

5. In combination, an electron emissive cathode, an electrode for emitting secondary electrons in response to impingement thereon of primary electrons from said cathode, a spacecharge grid interposed between the cathode and the secondary emission electrode and electrically connected to the latter, a grid-like anode between the grid and the secondary emission elec: trode for receiving secondary electrons from the latter, a load device connected in circuit with the anode, a control grid between the cathode and the space charge grid, the said control grid having its potential variable in response to a controlling influence which tends to approach a predetermined critical value so as to regulate the flow of primary electron current from the cathode, and means including a resistance connecting the cathode to the space charge grid and the secondary emission electrode for making their potential predominantly a function of the primary electron current, the resistance being such that upon the attainment of the said predetermined value of the said controlling influence the space charge grid becomes effective completely to block the flow of primary electrons and thus to prevent the further supply of current to the load device.

LEWIS R. KOLLER. RALPH. P. JOHNSON. 

